1. Field of the Invention
This invention relates to a multi-functional ruler including axial seats, an axial rod, an axial nut and a roller.
2. Background of the Invention
A multi-functional ruler 40 presently on sale in the market is indicated in FIG. 1, wherein it can be seen that axial seats 41 and 42 are set on the body of the ruler 40, and a roller axial rod 30 is set on the forementioned axial seats 41 and 42. The roller axial rod 30 is formed by an internal shaft 31 which extends through an external shaft 32 and also rollers 33 and 34 which are connected by threads set separately on its two ends to internal shaft 31.
During use of the prior art ruler, the user can press the body of the ruler 40 lightly to cause the ruler to slide forward and backward. Being fixed to the axial seats 41 and 42 of the body of the ruler, the forementioned external shaft 32 will not slide. The internal shaft 31, which is set inside the forementioned external shaft 32, will follow the body of ruler 40 to enable the body of the ruler 40 to move smoothly. In spite of the fact that the roller axial rod 30 presently found on sale in the market does not incur wear and tear when the body of the ruler 40 slides since external shaft 32 is fixed into the axial seats 41 and 42 of the body of the ruler 40, and the upper, lower, front and rear direction of the forementioned rollers 33 and 34 are kept an appropriate distance from the body of the ruler 4, certain defects such as those set forth below exist:
1. Since internal and external shafts are employed by the multi-functional ruler currently on sale in the market to cause the roller to move through sliding, the surface of its internal shaft remains in touch with the internal edge of the external shaft. When the internal shaft is moving, it will cause a continuous friction with the external shaft. This frictional force will affect the smooth sliding of the internal shaft, and thus can directly hinder the work such as with engineering drawings.
2. Gaps are maintained at the periphery of the rollers on the axial rod. When the body of the ruler is sliding, due to the fact that only the external shaft of the axial rod is tightly squeezed against the interior of the axial seat on the body of the ruler, the axial rod can readily move transverse to its rolling movement, and thus will affect the precision of the drawings made. As indicated in FIG. 2, errors are found in the lines which are drawn with the help of this prior art ruler. Thus, such prior art rulers cannot achieve an accurate drawing effect.